1. Field of the Invention
The present invention relates to a wireless network consisting of a plurality of nodes. More particularly, the present invention relates to a method and system for reducing unnecessary power consumption of a node in a wireless network during a time slot reserved by the node.
2. Description of the Related Art
A wireless network typically consists of a plurality of nodes. The nodes of the wireless network transmit and receive data to and from one another. The node has a regulation in order to transmit and receive data. More specifically, data experience a collision on the network when at least two nodes transmit data at the same time, and thus, a receiver node receives error-containing data. Accordingly, the nodes in the wireless network have to avoid transmitting data at the same time.
A structure of a wireless network will now be described with reference to FIG. 1. FIG. 1 illustrates a wireless network consisting of nodes A to E. The nodes A to E are located within a predetermined area of a beacon section to transmit beacons. Referring to FIG. 1, the node A transmits beacons to the nodes B to E, and the node B transmits beacons to the nodes A and C. The node C transmits beacons to the nodes A and B, and the node D transmits beacons to the nodes A and E. The node E transmits beacons to the nodes A and D. The node C transmits data to the node B during a reserved time slot, and the node E transmits data to the node D during a reserved time slot.
FIG. 2 illustrates a super frame used in the nodes of the wireless network. As shown in FIG. 2, the super frame consists of 256 time slots for beacons and data. The nodes in the wireless network require synchronization information to synchronize with one another. Therefore, the node transmits a beacon to its neighboring nodes with the synchronous information being contained in a certain area of the beacon. The node that wishes to transmit data uses a reserved one among the 256 time slots to transmit the data.
For example, if the node C uses the time slot 2 to transmit data, the node B receives the data during the time slot 2. If the node E uses the time slot 3 to transmit data, the node D receives the data during the time slot 3. Generally, a sender node searches for a time slot its neighboring nodes have not reserved and asks a corresponding receiver node whether it is possible to reserve the searched time slot. If it is possible to reserve the time slot in question, the receiver node notifies the sender node of that the reservation of the time slot is allowed. If it is impossible to reserve the time slot in question, the receiver node notifies the sender node of that the reservation of the time slot is canceled. If the sender node and the receiver node agree with the reservation of the time slot, the sender node transmits data to the receiver node during the reserved time slot.
FIG. 3 illustrates an active period and an inactive period of the node C for transmitting data and the node B for receiving data. FIG. 3 also illustrates a super frame consisting of a beacon transmission section and a plurality of time slots. In this example, it is assumed that the node C has reserved the time slot 0 and the time slot 1 to transmit data to the node B.
The node C enters an active state during the reserved time slot 0 and time slot 1 to transmit data to the node B. The node B enters an active state during the reserved time slot 0 and time slot 1 to receive the data from the node C. However, the node C may not transmit all of the necessary data during the time slot 0 and the time slot 1. For example, if a wireless channel condition between the nodes C and B becomes worse, the node C may not transmit the necessary data. The node C has to remain in the active state even during the time slot 2 and the time slot 3 to know if the time slot reserved by nodes other than the node C is available. If a certain node reserves the time slot 2 and the time slot 3 but does not use the time slot 2 and the time slot 3, the node C transmits data during the time slot 2 and the time slot 3. The node B remains in the active state during the reserved time slot 0 and time slot 1, and returns to inactive state during the time slot 2 and the time slot 3. Accordingly, the node B can prevent unnecessary power consumption.
However, if a power of the node C is less than a predetermined set value, the node C wastes the power because the node C remains in the active state during the time slot 2 and the time slot 3 regardless of the state of the node B. Also, when the sender node C remains in the active state to transmit data although the receiver node B is in the inactive state, unnecessary power consumption is caused by the sender node C. Also, since another nodes wish to use the time slots 2 and 3 but they are not allowed to use the time slots 2 and 3, a wireless resource is wasted.